Electric fuse



E. V. SUNDT ELECTRIC FUSE March 9', 1943.

Filed July 25, 1942 fade/afar. Zdwczrd Yfizuzdi Jy- Patented Mar. 9, 1943 7 UNITED STATES PATENT OFFICE I y m fzusn I mm v. Sundt, Amen, c m. Application July 25, 1942, Serial No. 452,267

67m li t 11:11am embodiment of the element I! This invention relates to improvements in electric fuses. In electric fuses comprising fusible elements or links having the ends attached to terminals or end'caps of cartridge or capsulelike casings, failure of the elements frequently occurs due to crystallization resulting from repeated heating and cooling of the element. Generally such an element has a portion of minimum cross-section which determines the current carrying capacity of the fuse and which, upon momentary overloads, is heated to a relatively high temperature but below the fusion temperature of the fusible link material. As a result of the crystallization due to such repeated heating andcoolingofthefuselinkinuseandthemetal fatigue caused by the accompanying expansion and contraction of such links, breakage of the same when subjected to exteriorly imposed vibrations or shocks such as occur in use in aircraft and other installations is quite common. Where the ends of such a link are aihxed to end caps or fuse terminals with no provision made for accommodating longitudinal expansion as in conven tional cartridge fuses, the link generally buckles or bends at the hottest portion thereof which is also usually the weakest structural portion of the link, and hence the period of usefulness of such fuse frequently is terminated by breakage due to shocks or vibrations rather than to fusion under current overloads. Such breakage of fuse elements is particularly troublesome where the links are formed of low temperature metals such as zinc which, at temperatures at or above 350 0., become relatively weak structurally,

The object of the present invention isto provide a fuse having means which accommodates thermal expansion and contraction of the fuse element in such manner as to avoid flexing of the hottest and hence generally the most highly crystallized and weakest portion of the element for avoiding breakage thereof due to externally originated vibrations or to stresses set up in the element by the expansion and contraction there- In the accompanying drawing,

Figure 1 is a broken elevation of a fuse structure illustrative of the present invention;

Fig. 2 is a sectional view. taken on line 2-2 of Fi 1;

Fig. 3 is a perspective view of a detached fuse element of the type shown in Figs. 1 and 2.

In the drawing a cartridge or capsule-type fuse is illustrated comprising a glass or other protective tubular casing i0, and caps II and I2, and a fuse element indicated generally by numeral l3.

metal that occurs due to flexing take place not shown in the drawing. two pairs of wings l4, it are shown, each pair of which in end view are generally of Z shapa lhe ,outer longitudinal edges .IQ of the wings I and i5 slidably contact the interior wall of the casing Ill, and by supporting the element intermediate the ends thereof assist in reducing breakage of the element due to exteriorly imposed vibrations or shocks. The intermediate portion of the fuse element H is shown as being of reduced cross-sectional area and is the portion which determines the current carrying capacity of the fuse and which, in case of excessive current overloads, is the portion that fuses and opens the circuit. The portion ll of the fuse is therefore structurally the weakest P rtion of the fuse.

In the drawing the portion ll ,is shown as being twisted through an arc of about to give it a spiral form for stiffening it against flexing and thereby reducing or altering its tendency to vibrate. The free end of the wing sections ii of the fuse link or element is shown electrically connected to the end cap l2 preferably by solder It. At the other end of the fuse element the wings I terminate short of the end of the element which has a. terminal portion I! attached to the cap ll preferably by solder 20': The portion I9 is greater in cross-sectional area than the portion I1 and hence is heated less than the latter by current flowing through the link. The portion I9 is provided with a formation that enables it to accommodate the longitudinal expansion and contraction of the link that occurs when the link is subjected to temperature changes, the formation being shown as a reverse bend or goosenec l9.

Expansion of the conventional fuse link results in flexing or buckling of the structurally weakest portion, that is, the portion of smallest cross-Sectional area, which portion during the flow of current is also the hottest portion of the link. This hottest and weakest portion, therefore, tends to crystallize, which tendency is augmented by the flexing action that occurs in said portion during expansion and contraction of the fuse. hence such portions of the fuses frequently are broken by physical shock or vibration to which the fuses are subjected in use. In the present construction, while the portion ll of the fuse link becomes hottest in use, the bend or oose-neck portion l9 permits the section I! to flex to accommodate the expansion of the link, and hence any crystallization or fatigue of the bend l9, which, due to the flexibility imparted to the latter section, responds readily in accommodating longitudinal expansion of the link. While the bend or formation I9 has been termed a "goose-neck" due to the particular shape of the same shown in the drawing, it will be apparent that the object of such formation is to enable it v to flex readily under the expansive andcontractile forces exerted by the element as it becomes heated or as it cools and thereby reduces oreliminates the flexing and buckling movements and greater stresses that would otherwise occur in the structurally weaker portion II. It will be apparent that formations of other shapes which will accommodate longitudinal expansion or contraction of a fuse link for protecting a structurally weaker portion against flexing or buckling or rupture by reason of expansion and contraction of the link that occurs upon heating and cooling thereof may be employed without departure from the object and spirit of the present invention.

The use of non-integral springs attached to one end of a fuse link for accommodating expansion and contraction of the element has been avoided by the present improvements and a simple one-piece element is provided which can as readily be assembled within the cartridge or casing as a conventional one-piece element. However, the flexible spring-like formation l9 substantially decreases fatigue of that portion of the fuse which becomes hottest and most highly crystallized and brittle during use and hence reduces the susceptibility of the element to breakage by externally imposed vibrations and shocks as well as from stresses imposed on that portion of the element by longitudinal expansion and contraction of the element during use.

I claim:

1. A fuse of the capsule type comprising a casing and a one-piece fuse element therein, said element comprising a fusible portion of minimum cross-sectional area and a portion of greater cross-sectional area having a greater current carrying capacity than said other area andprovided with an integral formation rendering said latter portion sufficiently flexible to accommodate the longitudinal expansion and contraction of the element resulting from the heating and cooling thereof.

2. A fuse comprising a casing. end caps therefor, a one-piece fuse element therein having the ends attached to said caps, said element comprising a portion of reduced cross-sectional area that fuses upon excessive current overload and a portion of greater current carrying capacity, and means integral with the latter portion for accommodating the longitudinal expansion and contraction of the element accompanying the heating and cooling thereof.

3. A fuse comprising a casing, end caps therefor, a one-piece fuse element therein having the ends attached to said caps, said element comprising a portion of reduced cross-sectional area that fuses upon excessive current overload and a portion of greater current carrying capacity, and a reverse bend in said latter portion of the fuse elementre'ndering the same sufflciently flexible to accommodate longitudinal expansionand contraction of the element for avoiding the flexing'of said first mentioned portion upon expansion and contraction of the element.

4. A fuse comprising a casing, end caps therefor, anda fuse element in said casing having ends secured to said caps, said element being provided with a portion designed to fuse upon predetermined current overload and an integral formation in another portion thereof rendering the same sufficiently flexible to accommodate iongitudinal expansion and contraction of the element for avoiding flexing of said first mentioned portion of the element.

5. A fuse comprising a casing, end caps therefor, and a fuse link in the casing attached at the ends thereof to said caps,-said link comprising a weakened portion that fuses upon predeter- 'mined maximum current overload, said portion being spirally shaped for stiffening the same structurally, and an integral portion provided with a formation rendering said portion sufficiently flexible to accommodate longitudinal expansion and contraction of the link upon the heating and cooling thereof respectively for avoiding flexing of said weakened portion upon such expansion and contraction.

6. A fuse link having a fusible portion relatively weak structurally as compared with the current carrying remainder of the link, and an integral spring-like formation in a structurally stronger portion thereof rendering such latter portion sufficiently flexible to accommodate'iongitudinal expansion and contraction of the link for avoiding the flexing of said weaker portion during the expansion and contraction of the link that occurs upon the heating and cooling thereof.

EDWARD V. SUND'I. 

